1. Field of the Invention
The present invention is related to a calibration apparatus and method thereof.
2. Description of the Prior Art
Current balance is an important specification for an LED (Light Emitting Diode) driving circuit driving chains of LEDs. In conventional specification, the uniformity for the chains of LEDs is required to be within 1%. However, due to the variation in process parameters during manufacturing, the electronic components of the LED driving circuit may not be able to meet the specification of current balance.
FIG. 1 is a diagram illustrating conventional multi-channel LED driving circuit 100. Using power switch M1 and booster 11, input voltage Vin is boosted to the voltage level required for driving LED chains 13 and 14. Multi-channel driving circuit 12 is configured to control the channel current of transistors M3 and M4 using current driving circuits 15 and 16, respectively. Each of current driving circuits 15 and 16 compares the voltage signal fed back from corresponding resistors R1 and R2 with reference voltage VREF, thereby dynamically controlling the corresponding channel current and further stabilizing the current flowing through resistors R1 and R2. Ideally, if the resistance of resistor R1 equals to that of resistor R2, the current flowing through LED chains 13 and 14 may be equalized for achieving current balance.
However, error amplifiers OPA1 and OPA2 of multi-channel LED driving circuit 100 may not have ideal characteristics. Due to process variations, error amplifiers OPA1 and OPA2 may exhibit unmatched offset voltages, the difference between which is likely to hinder multi-channel LED driving circuit 100 from meeting the specification of current balance.